Change of shade of diazotype images by treatment with moist sulfur dioxide vapors



Patented Mar. 7?, 1950 CHANGE OF SHADE OF DIAZOTYPE IMAGES BY TREATMENT WITH MOIST SULFUR DIOXIDE VAPORS Sam Charles Slifkin, Binghamton, N. Y., assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application November 10, 1945, Serial No. 627,975

3 Claims.

This invention relates to the production of diazotype light-sensitive layers and particularly to the improvement of the image obtained by using such light-sensitive layers.

In the duplication of originals which are transparent or semi-transparent, such as tracings or engineering drawings and typewritten documents by the diazotype positive reproduction method, it is highly desirable that the image reproduced on the diazotype be one of high contrast. Accordingly, the selection of dye components for the production of the light-sensitive layer is limited to those components which will produce deep shades upon development of the image.

However, such reproductions, though of high contrast andhaving high visual density which admirably suitsthem for utility assingle copies. do not possess sufficient photographic density or opacity to ultraviolet light to render them suitable for use as intermediate copies in the further production of diazotype light-sensitive copies. It is often desirable and sometimes necessary to use a diazotype copy as a master copy or intermediate for the production of such further copies, particularly where the original to be reproduced is a valuable drawing or an original design made on a delicate material which would become damaged or destroyed by frequent use in the printing process.

It is essential in the so-called reflex diazotype copying process for the duplication of originals which are opaque to light or which transmit insufficient light to energize the light-sensitive surface of the reproduction media to make an intermediate copy on a transparent material which can be thereafter employed for the reproduction of a final diazotype copy or copies. In processes which have been heretofore developed for the production of such transparent intermediate copies, the light-sensitive layer contains a dye component or dye components which upon development will produce colors highly absorptive of actinic light. Such a process is described in United States Patent No. 2,245,628, issued June 17, 1941. The process described in said patent involves the coating of a suitable transparent base, such as regenerated cellulose or cellulose acetate, with a solution containing a diazo compound and an azo coupling component which upon development will yield a yellow to greenishyellow dye. The images produced by the exposure and development of the light-sensitive layers of this process are of very poor contrast and, because of this fact, the intermediate prints obtainable by the method of this patent are difficult to check for flaws in reproduction before using the intermediate for the production of final diazotype prints on opaque diazotype paper.

Diazotype light-sensitive layers have also been developed for use on thin or transparentized paper, using diazo compounds and azo coupling components which will reproduce the image in a sepia color. These light-sensitive layers may be employed as intermediates or master copies for the reproduction of valuable originals or designs on delicate materials in accordance with the or dinary printing-through method indicated above. These sepia images on transparentized paper are highly absorptive of actinic light or have a high degree of opacity to ultraviolet light, but share the same disadvantage of low contrast with the transparent intermediates of the reflex process of Patent No. 2,245,628. Thus, these sepia prints of high opacity to ultraviolet light are, nevertheless, difiicult to read and imperfections in the master copy or intermediate print are often overlooked and escape detection until subsequent copies of high contrast are made from them on diazotype reproduction paper which will reproduce the image in a deep color. Even then, it is often diflicult to determine whether the imperiection has been introduced during the reproduction of the original onto the intermediate copy or during the reproduction of the intermediate or master print onto the final copy.

In addition to the disadvantages inherent in the low contrast images of colors of high photographic density, such as sepia or brown dyes, these colors are also subject to a strong tendency toward precoupling of the dye components. Such colors are produced by using as coupling components resorcinol and derivatives of m-aminophenol which have a high coupling rate. Consequently, in the unexposed state, the dye components contained in the light-sensitive layer will tend to couple prior to use. Hence, these light sensitive layers will have a poor shelf life and must be used soon after the coating of the layer onto the transparentized paper or film base.

It has now been found that a diazotype lightsensitive layer on a transparent or semi-transparent base, such as transparentized paper, which will reproduce the image in a dark color of good contrast can be employed as an intermediate copy or master copy for the further reproduction of diazotype images, if the diazo compound employed in the light-sensitive layer for the production of such dark colors is such that the dye produced therefrom is sensitive to changes in pH. When such diazos are employed, together with couplers which will reproduce the image in a dark color, such as blue or blue-black, the image on the intermediate copy can be reproduced in the dark color in the usual way by first exposing either by the print-through or reflex method and then developing'by treatment of the exposed light-sensitive layer in an alkaline medium, such as an atmosphere of ammonia gas. produced blue image in the intermediate print is then further exposed to an acid atmosphere, such as the moist fumes of volatile acids. The dark colored image being sensitive to a change in pH, changes to a sepia or brown color, which The rehas high ultraviolet absorption characteristics,

under this acid treatment. Thus, bythis method it is possible to reproduce an original on a lightsensitive diazotype reproduction medium in a dark colored image which can be easily read, thereby rendering the detection of imperfections in the copy easy. The same intermediate copy which is originally developed in a color affording good contrast also performs the dual function of efliciently transmittingthe image onto further diazotype or other light-sensitive materials as final copies, due to its ability to become opaque to ultraviolet light after the acid treatment. The advantages of such a light-sensitive diazotype intermediate are at once obvious. As pointed out above, the detection of imperfections in the intermediate copy is simplified. A further advantage is presented in the fact that this diazotype paper can be used interchangeably for single copies of good contrast. or forv intermediate copies requiring the high. opacity to ultraviolet light caracteristic.

Thesepia. orv brown image produced by expo.- sure, of the developed dark colored diazotype imagesof this invention to acids may be reconverted to the original dark color by a second ex,- posure to alkalis, such as ammonia gas, after the intermediate sepia or brown colored print has served its purpose as a master print for producing additional copies. This process of converting the original dark colored image to an ultraviolet light absorbing sepia or brown and reconverting the latter to the original dark color can, of course, be repeated whenever desired. The sensitivity of the azo dye image to changes in pH is apparently a function of the diazo compound and, accordingly, diazo. compounds which are sensitive to changes in pH must be employed. As an illustrative or preferred class of such diazo compounds, I mention the diazo derivatives of pphenylene diamines or p-amino aniline compounds wherein the undiazotized amino group contains at least one alkyl substituent. Other substituents which may be substituted on the undiazotized amino group include aralkyl, cycloaliphatic and alkoxy groups. Examples of such preferred classes ofdiazo compounds are p-amino- N-methyl aniline, p-amino-N-diainethyl aniline, p-amino-N-ethyl aniline, p-amino-N-diethyl aniline, p-amino-N-ethylolaniline, p-amino-N-ethyl- N-ethylolaniline, 4-diazo-1-cyclohexyl an'iline, 4

diazo-l-dicyclohexyl aniline, 4-diazo-2-methoxy- 6 l-cyclohexyl aniline, and 1-amino-4-(dibrom- 2,6'-benzyl) amino benzene.

The coupling components which are employed in the light-sensitivelayers used in this process should be such as to produce with the diazo compound a dark colored and preferably a blue image. Examples of coupling components which will produce blue images with diazo compounds of the preferred classifications are the sodium salt of 2'-amino-8-naphthol-3,6-disulfonic acid (2R- 4 salt), 2,3-dihydroxynaphthalene, B-naphthol-3,6- disulfonic acid (R-acid) 2,7-dihydroxynaphthalene, 1,7-aminonaphthol, 2-hydroxynaphthalene-8-biguanide, 1-amino-8-naphthol-3,6-disulfonic acid, l-naphthol-l-sulfonic acid, and lnaphthol-3,8-disulfonic acid. Diazotype lightsensitive layers containing such couplers in combination with diazo compounds having the function of producing azo dyes sensitive to changes in pH" are relatively stable against premature coupling. Hence, in addition to the advantage of providing images having good contrast, but which .can be adapted to use where high opacity to ultraviolet light is required, these light-sensitive layers possess the property of long shelf life and can be used for long periods after they have been prepared and still give clear-cut images having no background color. Background color produced by premature coupling of the dye components in the light-sensitive layer prior to use is particularly objectionable in the case of prints which are to be used as intermediates for the further production of additional copies on diazotype or other light-sensitive medium, since any background color which appears in the intermediate print will act as an absorbent for ultraviolet rays and consequently will show up as an undesired design in the background of the final copy.

Any volatile acid may be employed as the acid medium for changing the pH sensitive image from a dark contrasty color to a sepia or brown which will have high photographic opacity. Moist sulfur dioxide fumes have been found to be best suited to this process because they do not have as great a weakening effect on the paper as the other acids and also because .of thebleaching effect. which sulfur dioxide hason a paper carrier.

It will be understood that this invention is not .limited to the preferred components of the lightsensitive layers or to the production of blue images as the contrasty color of the intermediate print. It will be further understood that the invention is not limited to the amounts or materials of the following example which is set forth here as illustrative of the best manner of carrying out the invention. In the following example, the parts are by weight unless otherwise stated.

Example A thin, transparent paper stock is coated by any of the known methods for applying diazotype light-sensitive coating solutions to a carrier with a solution having the following components:

R salt, 2 grams Boric acid, 3 grams Thiourea, 5 grams p-Diazo-N-diethylaniline, 6 grams Water to make 100 cc.

The coated paper is then dried and stored in a dark room. Upon exposing samples of the dried diazo sensitized paper under a diapositive and developing the image with gaseous ammonia, a dark blue print is obtained. This print is then placed in a chamber containing moist S02 fumes. The dark blue image immediately changes to a sepia color. The print now containing the sepia image is removed from the S02 exposure chamber and used as an original by exposing any ordinary diazotype light-sensitive paper to a source of ultraviolet light under the thus-produced sepia print. Upon development of the exposed ordinary diazotypecopy by treatment with gaseous ammonia, a clear, well-defined print of the original image is obtained. A number of such final prints can be printed from the sepia color intermediate produced by the sulfur dioxide treatment. After the desired number of prints have been obtained, the sepia dye image is then reconverted to its original blue tone by a second exposure to ammonia gas. This reconverted print can then be stored away for such future use as may be desired.

Samples of the original unexposed light-sensitive layer produced from the coating solution of this example, after storage in a dark room for long periods of time, can be used for the production of intermediate prints by exposure and development in an atmosphere of gaseous ammonia, followed by exposure of the developed print to an atmosphere of moist S02 fumes, with the same degree of success as the freshly coated and dried material.

Having now particularly set forth and described my invention and having illustrated the best method of performing it, what I now claim as new is:

1. The process of changing the shade of a blue azo dye diazotype image, the diazo component of which is a p-amino benzene diazo compound wherein the amino group is substituted at least once by an alkyl group and the coupling component is the sodium salt of fi-naphthol 3,6-disulfonic acid which comprises exposing the blue diazotype image to the moist vapors of 5 sulfur dioxide.

2. The process of changing the shade of a blue dye diazotype image the diazo component of which is p-diazo-N-diethylaniline and the cou pling component of which is the sodium salt of ,8-naphthol-3,S-disulfonic acid which comprises exposing the blue diazotype image to moist vapors of sulfur dioxide.

3. The process or" changing the shade of an azo dye diazotype image, the diazo component or" which is a p-amino benzene diazo compound wherein the amino group is substituted at least once by a member of the group consisting of alkyl, aralkyl, cycloaliphatic and alkoxy groups and the coupling component is a naphthol nuclearly substituted once by a member of the group consisting of hydroxy, amino, guanide and sulfonic acid groups and additionally substituted in up to two nuclear positions by a member of the group consisting of hydrogen and sulfonic acid which comprises exposing the diazotype azo dye image to moist vapors of sulfur dioxide.

SAM CHARLES SLIFKIN.

REFERENCES GITEID The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,926,322 van der Grinten Sept. 12, 1933 2,245,628 Poser June 17, 1941 2,418,623 Chechak Apr. 8, 1947 FOREIGN PATENTS Number Country Date 1,549 Great Britain of A. D. 1912 182,16? Great Britain June 21, 1922 

3. THE PROCESS OF CHANGING THE SHADE OF AN AZO DYE DIAZOTYPE IMAGE, THE DIAZO COMPONENT OF WHICH IS A P-AMINO BENZENE DIAZO COMPOUND WHEREIN THE AMINO GROUP IS SUBSTITUTED AT LEAST ONCE BY A MEMBER OF THE GROUP CONSISTING OF ALKYL, ARALKYL, CYCLOALIPHATIC AND ALKOXY GROUPS AND THE COUPLING COMPONENT IS A NAPHTHO NUCLEARLY SUBSTITUTED ONCE BY A MEMBER OF THE GROUP CONSISTING OF HYDROXY, AMINO, GUANIDE AND SULFONIC ACID GROUPS AND ADDITIONALLY SUBSTITUTED IN UP TO TWO NUCLEAR POSITIONS BY A MEMBER OF THE GROUP CONSISTING OF HYDROGEN AND SULFONIC ACID WHICH COMPRISES EXPOSING THE DIAZOTYPE AZO DYE IMAGE TO MOIST VAPORS OF SULFUR DIOXIDE. 